1. Field of the Invention
The invention relates generally to signal processors for mobile communication and to corresponding digital methods for evaluating mobile communications reception signals. In particular, the invention relates here to signal processors and methods in which mobile communications reception signals of different mobile phone standards are received and evaluated with corresponding digital circuits which are integrated on a single chip.
In the GSM standard which is currently used in mobile communication, so-called GMSK (Gaussian Minimum Shift Keying) modulation is used. The modulation employs a signal space with signal points which have a phase difference of 180°. For this purpose, the GPRS packet service (General Packet Radio Service) has been developed, which service renders it possible to operate at relatively high data rates. The further currently used standard which is known is the TIA/EIA-136-(IS-136-) standard in which a π/4 DQPSK (D quaternary PSK) modulation method is used to generate the transmission signals. The EDGE standard and the associated EGPRS (Enhanced GPRS) packet service were defined to a certain extent as a transitional standard between GSM and GPRS on the one hand and UMTS on the other. EDGE is still a TDMA (Time Division Multiple Access) method but a change over from GMSK modulation to 8-PSK modulation is already taking place. In 8-PSK modulation, a signal space with 8 signal points is used, the phase difference between the individual signal points being 45°.
A general objective in mobile communications is to develop mobile communications devices which are configured for operation with a plurality of different mobile phone standards and can therefore be used in the various mobile phone systems. This requirement is fulfilled in the baseband processors PCI 3700 and PCI 3800 from PrairieComm for GSM and TIA/EIA-136 and for GSM, EDGE and TIA/EIA-136 by using a separate specific signal processing architecture for each mobile phone standard both for the generation and the evaluation of the digital signals, and by supplying the signal processing architecture with a signal clock rate which is precisely matched to the respective mobile phone standard.
As mentioned above, the problem here is the fact that at the reception end the evaluation methods also require different signal clock rates. This problem has been solved hitherto—as for example in the baseband processors PCI 3700 and PCI 3800 from PrairieComm for GSM and TIA/EIA-136 and for GSM, EDGE and TIA/EIA-136 mentioned above—as at the transmitter end in that a plurality of different clock frequency generators and correspondingly different signal processing architectures have been used for the individual mobile phone standards. However, the result of this is that a plurality of circuit blocks are necessary for similar functions and have to be supplied with different signal clock rates. As a rule, this means there is an increased demand for components and for chip area. Operating with different system clock rates thus makes it more difficult to integrate the functions in one component. Owing to the separate processing with different clock rates it is generally also impossible to use a uniform interface to transfer the reception signals, which are supplied by the assemblies for transposition from the carrier-frequency position into the equivalent low pass position, so that there is usually also a need for a plurality of different A/D converters to which the reception signals have to be transferred via a plurality of interfaces.